# Catapult ## Description： A catapult is a ballistic device used to launch a projectile a great distance without the aid of gunpowder or other propellants – particularly various types of ancient and medieval siege engines. ... We will make a catapult with LEGO building blocks. Equipped with servos and gears, the car has LEGO tower used to carry projectiles. As the servo rotates to a proper angle then push the long arm backward a projectile will be launched. ## How to build up a catapult Step 1 Required components ![3](media/ef12c46a8dc6e5f5c7f7ee6fc3c3dc55.png) ------ ![3_1](media/85116f87b7e67a5ab0de47507da771aa.png) ------ ![3_2](media/bb5d2d9bc07a9cfdc997f798c6c56eca.png) ------ Step 2 Required components ![3_3](media/d827f9196a2aed7686c9d767e64b7f66.png) ------ ![3_4](media/7e4fed5d035aac6b58ee79afd3aca1a1.png) ------ ![3_5](media/088c8c481e0b48b3625f465a4ceed269.png) ------ Step 3 Required components ![3_6](media/52da40da0bbeae39083c81a57c1117e6.png) ------ ![3_7](media/42004639ab3aaca47c5121bf7ac18a2d.png) ------ ![3_8](media/08f91fa357f53479f8a121bd2b6d8883.png) ------ Step 4 Required components ![3_9](media/1678f2dcaaed186ba12fbcbc9a6d34c2.png) ------ ![3_10](media/8b54d0c59f13bbbc54fafefec90bbb24.png) ------ ![3_11](media/b2900c9594fb64b10ee734e2a533cfbf.png) ------ Step 5 Required components ![3_12](media/9975825da874d5431f9e672ca9a4479e.png) ------ ![3_13](media/5c41a82613abc2c43016fb25edc5c68c.png) ------ ![3_14](media/08ebb224d83a88b37ebd8b5cb80bb3ad.png) ------ Step 6 Required components ![3_15](media/9c247eddce7a872899c34e013e12db31.png) ------ ![3_16](media/3a2946b85862bf346ffab23458553bb3.png) ------ ![3_17](media/531619d92526f175188479be5fe9c403.png) ------ Step 7 Required components ![3_18](media/76541a6311535fd572743b0ad47f1254.png) ------ ![3_19](media/a75726411d9f0bcccda1600a3f3b3cdc.png) ------ ![3_20](media/216440c8133bb1fa5f9670d084815ee6.png) ------ Step 8 Required components ![3_21](media/7e7a7032c111bbfc5e4a6605abb84dd7.png) ------ ![3_22](media/b933ff3a1efee59f590e3d511c1d2864.png) ------ ![3_23](media/be75847ab4f10c2750868daf02cad97d.png) ------ Step 9 Required components ![4](media/8a0a23b5a1a7a332209e87d032815609.png) ------ ![4_1](media/5887d93dd221b4c3aeb7dcfe2a466846.png) ------ ![4_2](media/dae339a4baed35100a3580384bf228db.png) ------ Step 10 Required components ![4_3](media/a376478c51daef7b169d65b91257cff1.png) ------ ![4_4](media/ea08ecc209960e32eee4c930201c6112.png) ------ ![4_5](media/03394d1ec20bdfec33c01fcbaca3272a.png) ------ Step 11 Required components ![4_6](media/ccbf96f8a832f1b7429dd84c5d4345c8.png) ------ ![4_7](media/e4eeea6acd26fc704b516a4eed86d280.png) ------ ![4_8](media/275b434c0be9b0b29b0414c86f8016dd.png) ------ Step 12 Required components ![4_9](media/b7dcfd9502c3fd7b10667b6c8e02d9c2.png) ------ ![4_10](media/0805a74bbabfd014c772223f269034e6.png) ------ ![4_11](media/997424695d7920037017741fdbba2fac.png) ------ Step 13 Required components ![4_12](media/6348991aedca79b2dd8d672bf92a11d5.png) ------ ![4_13](media/a6b15b1c9cf2b4c57eb99613f3b101c4.png) ------ ![4_14](media/dc88133e92982bd31fecefee7ad8a7c1.png) ------ Step 14 Required components ![4_15](media/4647a2f97a30479a02a9166625ff8691.png) ------ ![4_16](media/cca8268d5c1cea871a6724f38440bf44.png) ------ ![4_17](media/ff899bedee462220afed7d6b57e5c4fb.png) ------ Step 15 Required components ![4_18](media/2ff9dd7a9593ae1d87ee1ef78f5ec79c.png) ------ ![4_19](media/2c0b652b42d4695eaeaf57802f7d0ab7.png) ------ ![4_20](media/7e28f9049c1d8081f7bb24b07c75471f.png) ------ Step 16 Required components ![4_21](media/f62f9d4b93b1b0ac66738baa034e710d.png) ------ ![4_22](media/3f1f8d3bfd3dd6c810d55ffceefe6ca3.png) ------ ![4_23](media/857bff0ba903623bc8d3a44d6410d828.png) ------ Step 17 Required components ![4_24](media/4d37a7993b087fe97734443ddb940941.png) ------ Set the angle of the servo to 180 degree | Wire servo up Servo | PCB Board | | :--: | :--: | | Brown | G | | Red | 5V | | Orange| S2（GPIO23）| Upload the code of the servo to the main board of the Beetlebot car, as shown below #include Servo lgservo; // create servo object to control a servo void setup() { lgservo.attach(3); // attaches the servo on pin 3 to the servo object } void loop() { lgservo.write(0); // tell servo to go to position } ------ ![4_25](media/9f5a242786bc3789adf9cf5e18b8ba51.png) ------ ![4_26](media/ac803fd31a550ed4dd380b0684019011.png) ------ Step 18 Required components ![4_27](media/b3f95a18ac4bc0caa38a2247766520cf.png) ------ ![4_28](media/9cce844758b800937ca64b05aff685d8.png) ------ ![4_29](media/35a51fcf6c258efb5b657d54bb3de756.png) ------ ## Wire up Interface the servo ![1ce70f3a2988e646798cadfc6fc8995](media/89fd41d160d778d0a7ef66c90fd28889.jpeg) ## Test Code： #include Servo lgservo; #define ML 15 #define ML_PWM 17 #define MR 14 #define MR_PWM 16 #define servo2 3 char val; char wifiData; boolean servo_flag = 1; void setup() { Serial1.begin(9600); pinMode(ML, OUTPUT); pinMode(ML_PWM, OUTPUT); pinMode(MR, OUTPUT); pinMode(MR_PWM, OUTPUT); lgservo.attach(3); lgservo.write(0); } void loop() { if(Serial1.available() > 0) { val = Serial1.read(); Serial.print(val); } switch(val) { case 'F': car_forward(); break; case 'B': car_back(); break; case 'L': car_left(); break; case 'R': car_right(); break; case 'S': car_stop(); break; case 'p': lgservo.write(85);servo_flag = 1; break; case 'x': servo_down(); break; } } void servo_down() { while( servo_flag == 1) { for(int i=55; i>0; i--) { lgservo.write(i); delay(2); } servo_flag = 0; } } void car_forward() { digitalWrite(ML,LOW); analogWrite(ML_PWM,255); digitalWrite(MR,LOW); analogWrite(MR_PWM,255); } void car_back() { digitalWrite(ML,HIGH); analogWrite(ML_PWM,0); digitalWrite(MR,HIGH); analogWrite(MR_PWM,0); } void car_left() { digitalWrite(ML,HIGH); analogWrite(ML_PWM,150); digitalWrite(MR,LOW); analogWrite(MR_PWM,105); } void car_right() { digitalWrite(ML,LOW); analogWrite(ML_PWM,105); digitalWrite(MR,HIGH); analogWrite(MR_PWM,150); } void car_stop() { digitalWrite(ML,LOW); analogWrite(ML_PWM,0); digitalWrite(MR,LOW); analogWrite(MR_PWM,0); } Build up a few target objects with building blocks(object A, B, C, D, E) and keep them in a certain distance away the catapult and connect Wifi. Click ![](media/5f365b2083f264b4ecfc5e68d07df287.png) to make the car to face the object A, hold down the button ![](media/0e62c323c0018af1a2824a120d447bda.png)to drive the catapult to launch a building block. Then release the button ![](media/0e62c323c0018af1a2824a120d447bda.png)to make the long arm return to the original state. Next, let’s check if the object A is hit by the launched block You can repeat above steps to hit the object B, C and D